1. Field of the Invention
The present invention relates to a circuit for pumping up current of an output port and a remote controller having the same, and particularly, to an output current pumping circuit, in which the output port of the present invention detects a level of power voltage with respect to drop of the power voltage and boosts and supplies the voltage to obtain output current of high voltage.
2. Description of the Related Art
Generally, if one or more keys are input through a keypad of a matrix structure in a remote controller, output ports of the key matrix are sequentially turned into a low state one by one by a port control unit, and each of the key inputs is read through a key input port having a structure having a pull-up resistor embedded therein. If a low input is read, a transmission signal of a predetermined format is generated at relevant output and input ports, and an output n-channel MOSFET (NMOS) transistor 100 embedded in an integrated circuit (IC) as shown in FIG. 1 or an output bipolar transistor 290 installed outside of the IC as shown in FIG. 2 is driven to turn on and off an infrared light emitting diode (LED) 110 and 210, whereby the generated signal can be transmitted to a device to be controlled that is apart at a certain distance. At this time, the maximum distance to which the signal can be transferred is referred to as a transmission distance, and the transmission distance is proportional to power voltage, and to current driven at the output NMOS transistor or the output bipolar transistor.
Accordingly, there will not be a problem when the power voltage VDD is high (in a high voltage state). However, if the power voltage is low (in a low voltage state), there is a problem in that capability of a current driver of the output NMOS transistor 100 or the output bipolar transistor 290 is distinguishably dropped, and thus, it is difficult to obtain high current of high voltage, whereby the transmission distance is also decreased.
In addition, a conventional pull-up resistor embedded in the key input port unit for reading key inputs from the key matrix 170 and 270 generally uses a single p-channel MOSFET (PMOS) transistor having an extended length equivalent to resistance, such as a PMOS transistor (14th MOS transistor) 710 shown in FIG. 3, and the pull-up resistor is turned on and off by controlling the gate of the PMOS transistor 710 in response to a control signal pull-up_enb. The resistance of the pull-up resistor has a characteristic of being inverse proportional to the power voltage. Particularly, since the resistance is adjusted to the operation performed under a condition of a power voltage of about 3V, the resistance is abruptly increased at a low power voltage of about 1.5V or less. Therefore, there is a problem in that since the conventional pull-up resistor has a resistance close to that of an off resistor of a key in the key matrix, the input port An is read as a low state even when the key is off, and thus, the IC mistakenly recognizes the key as being turned on.